I too have filled out the form for the Garmin and the STec. I installed the 55x recently and I am very happy. I won't upgrade to the 3100.
I saw this ad today in Barnstormers and they claim it has a Garmin autopilot. Someone might want to check this out and see why this 337 has a Garmin autopilot.
https://www.barnstormers.com/classif...ml?catid=17416